Purpose: Humerus varus caused by growth arrest of the medial proximal humeral physis is associated with upper limb length discrepancy and limitations in shoulder motion. The purpose of this study was to assess the results of proximal humeral valgus osteotomy for the treatment of humerus varus in skeletally immature patients. Methods: Six patients were treated at our institution between 1994 and 2006. The average age at the time of surgery was 13 years (range, 9-17 years). The causes of humerus varus were posttraumatic physeal arrest (n = 2), infection (n = 2), acquired physeal arrest secondary to a benign bone cyst (n = 1), and idiopathic cause (n = 1). All patients underwent proximal humeral valgus osteotomy with tension-band fixation. The average clinical and radiographic follow-up period was 21 months (range, 3-81 months). Results: All patients achieved bony union. Mean forward flexion improved from 76 degrees preoperatively (range, 45-100 degrees) to 148 degrees postoperatively (range, 100-180 degrees) (P = 0.01). Mean abduction improved from 63 degrees preoperatively (range, 30-100 degrees) to 116 degrees postoperatively (range, 90-160) (P = 0.02). Radiographically, the mean humeral neck-shaft angle improved from 95 degrees preoperatively (range, 75-105 degrees) to 130 degrees postoperatively (range, 112-160 degrees) (P = 0.001). Two patients had soft tissue irritation from the tension-band pins, which resolved with subsequent pin removal. Conclusions: Valgus osteotomy with tension-band fixation is an effective means of improving shoulder function and humeral neck-shaft angle in skeletally immature patients with proximal humerus varus.